IR text tests: Stable blank lines between declarations in class

Rework rendering of kt-like dump and signatures dump in order to avoid
unstable blank line between declarations of the same level:
1. No blank line for the first declaration inside the member scope of
the class.
2. Always a single blank line between each two subsequent declarations
inside the member scope of the class.

compiler/testData/ir/irText/declarations/delegate/delegationEvaluationOrder1.sig.kt.txt

@@ -66,6 +66,7 @@ class Derived : DerivedBase, Base {
   //   Public signature: foo/Derived.<init>|-5645683436151566731[0]
   //   Public signature debug description: <init>(){}
   constructor() /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: foo.Derived#foo(kotlin.String){}kotlin.String
   //   Public signature: foo/Derived.foo|-5534735991146511619[0]
@@ -87,6 +88,7 @@ class Derived1 : DerivedBase, Base {
   //   Public signature: foo/Derived1.<init>|-5645683436151566731[0]
   //   Public signature debug description: <init>(){}
   constructor() /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: foo.Derived1#foo(kotlin.String){}kotlin.String
   //   Public signature: foo/Derived1.foo|-5534735991146511619[0]
@@ -115,7 +117,6 @@ open class DerivedBase {
 //   Mangled name: foo.Base
 //   Public signature: foo/Base|null[0]
 interface Base {
-
   // CHECK JVM_IR:
   //   Mangled name: foo.Base#foo(kotlin.String){}kotlin.String
   //   Public signature: foo/Base.foo|-5534735991146511619[0]